U.S. patent number 5,248,657 [Application Number 07/699,035] was granted by the patent office on 1993-09-28 for method for forming internally helixed high temperature superconductor assembly.
This patent grant is currently assigned to General Dynamics Corporation, Space Systems Division. Invention is credited to Richard E. Bailey, Foster M. Kimball, Eddie M. Leung, Robert D. McConnell.
United States Patent |
5,248,657 |
Bailey , et al. |
September 28, 1993 |
Method for forming internally helixed high temperature
superconductor assembly
Abstract
A superconducting conductor assembly using high temperature
materials. A double-walled tubular structure has at least one
helical strip of superconductive material on the inner wall of the
inside tube. Brittle, non-ductile superconducting materials may be
used. A coolant, typically liquid nitrogen, is circulated between
the tubes to maintain the superconductor below the critical
temperature of the superconductor. A buffer layer is preferably
included between tube wall and superconductor. A plurality of
alternating layers of buffer and superconductor may be used.
Inventors: |
Bailey; Richard E. (San Diego,
CA), Kimball; Foster M. (San Diego, CA), Leung; Eddie
M. (San Diego, CA), McConnell; Robert D. (Denver,
CO) |
Assignee: |
General Dynamics Corporation, Space
Systems Division (San Diego, CA)
|
Family
ID: |
24807673 |
Appl.
No.: |
07/699,035 |
Filed: |
May 13, 1991 |
Current U.S.
Class: |
505/412;
219/121.68; 257/E39.018; 427/237; 427/239; 427/419.2; 427/419.3;
427/62; 505/410; 505/473; 505/477; 505/701; 505/704; 505/728;
505/730 |
Current CPC
Class: |
H01L
39/143 (20130101); H01L 39/2464 (20130101); Y10S
505/73 (20130101); Y10S 505/701 (20130101); Y10S
505/728 (20130101); Y10S 505/704 (20130101) |
Current International
Class: |
H01L
39/14 (20060101); H01L 039/24 (); B05D
005/12 () |
Field of
Search: |
;505/1,730,704,728
;427/62,63,419.2,419.3,237,239 ;174/125.1 ;219/121.68 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
Asano et al, "High Tc oxide superconducting films for RF cavities",
Proc. Workshop RF Supercond., 4th, 1989, vol. 2, pp. 723-743, 1990.
.
Yan et al, "Water interaction with the superconducting YBa.sub.2
Cu.sub.3 O.sub.7 phase", Appl. Phys. Lett. 51(7) Aug. 1987 pp.
532-534..
|
Primary Examiner: King; Roy
Attorney, Agent or Firm: Duncan; John R.
Claims
We claim:
1. The method of manufacturing a high temperature superconductor
assembly which comprises the steps of:
(a) depositing a substantially uniform layer of buffer material on
the inside wall of a first tube;
(b) depositing a substantially uniform high temperature
superconductor layer on said layer of buffer material;
(c) repeating steps (a) and (b) at least one additional time;
and
(d) scribing through all layers except the buffer layer deposited
on said inside wall to form a plurality of stacked substantially
parallel helical superconductor strips.
2. The method according to claim 1 further including providing a
second tube surrounding said first tube and introducing a flow of
coolant between said first tube and second tube at a temperature
sufficient to maintain said superconductor layer below the critical
temperature.
3. The method according to claim 1 further including maintaining a
vacuum or inert gas within said first tube.
Description
BACKGROUND OF THE INVENTION
This invention relates in general to superconducting electrical
conductors and, more specifically, to a tube having a high
temperature superconductor formed along a helical internal
path.
Materials which have superconducting properties; that is, have
essentially no resistance at very low temperatures, have been known
for some time. Superconductors have been used in a number of
devices that take advantage of two unique properties of
superconductivity, low (ideally zero) power consumption and the
compactness possible with superconductors because of the absence of
power dissipation losses and their high current density.
Ductile alloys of niobium and tin, titanium, tantalum, zirconium
and other metals have been used in electromagnets in medical
apparatus, experimental devices in physics, for energy generation
in magnetohydrodynamic generators and are proposed for use in
levitating trains and many other purposes. Unfortunately, these
materials are superconducting only at temperatures below about 20K.
and must be constantly cooled by liquid helium during use. Liquid
helium is expensive and difficult to handle.
A number of "high temperature" superconducting ceramic materials
were discovered in the late 1980's. "High temperature" is a
relative term and now is generally taken to mean any temperature
above the boiling temperature of liquid nitrogen, 78.degree. K. The
best known of these new superconductors contain one atom of a rare
earth metal such as yttrium, two barium atoms, three copper atoms
and about seven oxygen atoms and is referred to as a "1-2-3"
superconductor. Other high temperature superconductor systems
include bismuth-strontium-calcium-copper-oxide and
thallium-barium-calcium-copper-oxide materials. It is expected that
additional ceramic superconducting materials will be
discovered.
While these high temperature superconductors have varying desirable
characteristics, primary of which is the high superconducting
transition temperature, they also have a number of drawbacks
limiting their rapid introduction into commercial products. A major
problem is material brittleness and lack of ductility, which
prevents the convenient production of wires, filaments and the
like. Also, these materials tend to have low critical current
density, often less than 1000 A/sq. cm. These problems have
prevented the use of these materials in such applications as large
superconducting magnet coils and power transmission lines.
Thus, there is a continuing need for improved methods and apparatus
which permit the use of the high temperature superconductors in
such devices.
SUMMARY OF THE INVENTION
It is, therefore, an object of this invention to provide a
conductor configuration that overcomes the above-noted problems.
Another object is to provide a conductor configuration that fully
supports brittle superconductors. A further object is to provide a
high temperature superconducting conductor having integral cooling.
Yet another object is to provide a conductor configuration which
improves the current density available with high temperature
superconducting materials.
The above objects, and others, are accomplished in accordance with
this invention by an internally helixed conductor having a double
walled tubular structure with thin film strips of superconducting
material deposited on the inside wall of the inner tube in a
helical pattern. Coolant, typically liquid nitrogen, is circulated
between the walls of the inner and outer tubes to maintain the
superconductor below the critical temperature. Any suitable
superconductor may be used. The assembly of this invention is
particularly adapted for use with high temperature superconductors
such as yttrium-barium-copper oxide,
barium-strontium-calcium-copper oxide and
thallium-barium-calcium-copper oxide and similar materials. For the
purposes of this application "high temperature superconductor" is
considered to be those having a critical temperature above about 90
degrees Kelvin.
The strips of superconducting material may be single or multiple
depending on the desired current capacity. The helical strips may
be formed by any suitable method, such as lithographic techniques,
chemical vapor deposition or the like, or application of uniform
coatings followed by helical scribing using mechanical or laser
processes. For best results, a layer of a material such as silver,
titanium or nickel alloys, sapphire and combinations thereof, which
is compatible with the superconductor may be applied on the inside
wall of the inner tube followed by application of the
superconductor over this buffer layer. Such buffer layers mitigate
differences in thermal expansion between the superconductor and
tube, provide protection against detrimental diffusion of tube
elements (e.g., aluminum) into the superconductor and contribute to
the crystalline formation of the superconductor layer. The
crystallinity of the superconductor layer is desirable since better
superconducting properties (e.g., higher critical current
densities) are associated with larger crystalline grains within the
layer. Additional layers of buffer and superconductor may be
deposited and connected in parallel to provide higher current
density.
The material and sizes of the tubes are selected to provide
necessary containment of Lorentz forces during operation. Typical
materials from which these tubes could be made include stainless
steels, copper, aluminum and alloys thereof. Fiber reinforced resin
composite materials may also be useful. The internal volume of the
inside tube, within the superconductor layer(s) may be filled with
an inert gas such as helium or nitrogen, to avoid degradation of
the superconductor. The resulting tubular conductors may be used,
for example in the manufacture of superconducting magnets,
electrical transmission lines, etc.
BRIEF DESCRIPTION OF THE DRAWING
Details of the invention, and of preferred embodiments thereof,
will be further understood upon reference to the drawing,
wherein:
FIG. 1 is a transverse section view of the tubular conductor of
this invention;
FIG. 2 is a section view taken on line 2--2 in FIG. 1;
FIG. 3 is an end view of a second embodiment of the conductor,
showing multiple superconductor strips;
FIG. 4 is a section view taken on line 4--4 in FIG. 3; and
FIG. 5 is an enlarged detail section view of a portion of the
tubular conductor assembly taken perpendicular to the tube
axis.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
Referring now to FIGS. 1 and 2, there is seen a double walled
tubular structure 10 having an outer wall 12, an inner wall 14 and
a space 16 therebetween. The two walls can be maintained in their
proper relationship by any conventional spacer means, such as a
plurality of small buttons or other spacers (not shown) at suitable
locations along and around the interior surface of tube 12. Tubes
12 and 14 may be formed from any suitable material. Typical
materials include metals such as aluminum, stainless steel, copper
nickel, titanium alloys and fiber reinforced resin composite
materials and combinations thereof.
A single strip 18 of superconducting material is applied to the
inside wall of tube 14 in a helical path as seen in FIG. 2. In most
cases it is preferred that the strip of superconducting material be
applied over a strip of a buffer material which avoids any
interaction between the material of tube 14 and strip 18. Any
suitable superconducting material may be used. Typical
superconductors include the brittle "high temperature"
superconductors such as yttrium-barium-copper oxide and the like.
Any buffer material may be used which is compatible with the
superconductor selected and the tube material. Typical buffer layer
materials include silver, nickel and titanium alloys, sapphire and
combinations thereof.
In order to protect the superconductor from degradation during use,
it is preferable to either maintain a vacuum in interior space 20
or to fill that space with an inert gas such as helium, argon, or
neon. Coolant is circulated through the space 16 between tubes 12
and 14. For present high temperature superconductors, liquid
nitrogen is effective. Other coolants may be used if desired,
depending upon the critical superconducting temperature threshold
for the superconductor used.
A plurality of parallel superconducting strips 18 may be used as
shown in FIGS. 3 and 4 to increase current density. Closely spaced
superconductor strips may be formed by coating the entire inside
wall of tube 14 with a buffer layer (if used) then coating the
buffer layer with the selected superconductor. Closely spaced
helical lines are then scribed through the superconductor and
buffer layers by mechanical scribing, laser scribing or any other
suitable method. The scribing separates the layers into plural
parallel strips.
In order to further increase current density, a multi-layer buffer
and superconductor configuration may be used, as illustrated in
FIG. 5. Here, alternating layers of buffer material 24 and
superconducting material 26 are applied to the inside surface of
tube 14. These layers may be applied using any suitable stencil or
other pattern forming technique with chemical vapor deposition,
plasma deposition or any other suitable method. Or, the entire
inside surface of tube 14 may be coated with the succession of
layers, then the helical pattern may be scribed through the entire
multi-layer configuration, as discussed above.
While various specific configurations, materials and arrangements
were described in the above description of preferred embodiments,
those may be varied, where suitable, with similar results. Other
applications, ramifications and variations of this invention will
occur to those skilled in the art upon reading this disclosure.
Those are intended to be included within the scope of this
invention as defined in the appended claims.
* * * * *